In my co-pending U.S. patent application mentioned above, there is disclosed an ultra-light aircraft wherein a hang cage is suspended from a collapsible Rogallo type wing by a main hinge assembly. The wing includes a longitudinal keel of light-weight tubular construction, leading edge members and a cross brace. A flexible lifting panel is secured along and between these members to establish a lifting surface. The hinge is clamped to the keel permitting free rotation of the wing about a spanwise axis extending longitudinally through the cross brace.
Rotation of the wing without pilot intervention induced by positive or negative wind gusts striking the flexible panel causes the angle of incidence or pitch between the wing and hang cage to vary so that the wing presents a constant angle of attack to relative wind enabling the aircraft to be essentially stall-free during flight. A cable and spreader tube arrangement interconnecting forward and trailing ends of the keel to the cross brace undergoes tension and compression loading to distribute bending stress acting on the keel during excessive wing loading to other parts of the aircraft.
The aforesaid spreader tube and cable arrangements operate satisfactorily to alleviate excessive aerodynamic wind loading in the hinged Rogallo wing of my prior invention without interfering with rotation of the wing. However, I have found that the aforesaid arrangement will not operate satisfactorily to alleviate excessive wing loading in conjunction with a rigid wing hinged to a hang cage due to their aerodynamic and structural differences with flexible wings, as described below.
A rigid wing generally comprises a pair of forward and rear tubes paired together on each side of the aircraft to establish leading and trailing edges of the wing. The paired forward and rear tubes are connected together by short longitudinal tubes bent in the shape of an airfoil with a single layer of fabric (e.g., Dacron) stretched across the resulting wing frame to establish lifting surfaces. Each pair of forward tubes are preferably connected together as is each pair of rear tubes so that the wing assumes a predetermined dihedral relative to the horizontal for improved stability during flight.
In conventional ultra-lights, the aforesaid rigid wing is fixed to struts extending upwardly from the hang cage so that the wing is non-pivotal in nature. A kingpost extends vertically upward from the wing. A pair of cables or landing wires respectively connect the leading and trailing edges of each wing tip to the kingpost. The cables are tensioned and are of different length so that the wing tip assumes a preset angle of pitch relative to a horizontal plane passing through the longitudinal axis of the fuselage or hang cage. A second pair of landing wires connect leading and trailing edges of an intermediate section of each wing to the kingpost. The second pair of landing wires are also of different length from each other so that the intermediate section of the wing assumes a preset angle of pitch that is greater than the wing tip angle of pitch. In other words, due to the inherent flexibility of the tubular members establishing the wing frame, each wing is `twisted` a small predetermined amount by the landing wires relative to a horizontal plane, so that the angle of pitch gradually decreases from the wing root proximate the keel to the tip. Corresponding first and second pairs of cables or flying wires project downward to connect the tip and intermediate sections of each wing to the hang cage to assist the landing wires in establishing wing twist and dihedral.
Wing twist characteristics are important to allow the tip sections of the rigid wing to assume a lower angle of attack with relative wind during flight than inboard sections of the wing. Thus, should the wing approach a stall condition during flight, the tip sections are less likely to stall than the inboard sections so that aircraft remains controllable. The flying and landing wires also assist in transmitting to the hang cage bending stress or excessive wing loading induced by upward or downward wind gusts striking the wing.
To obtain a rigid, free wing ultra-light configuration, it is not possible to modify the aforesaid conventional fixed wing design simply by hinging the rigid wing to the hang cage. This is because each flying and landing wire attached to forward and trailing edges in the conventional, rigid wing ultra-light described above is of fixed effective length that would tend to prevent the wing from rotating about a spanwise axis when the wings are designed with twist and/or dihedral in the manner described above. Since rigid wings are most efficient and give better control than flexible wings, and are commercially preferred, a freely rotatable, rigid wing ultra-light would be desirable to obtain the advantages afforded by free wings and rigid wings.
It is accordingly an object of the present invention to provide an improved free wing especially for ultra-light aircraft as well as for conventional aircraft employing a wing having dihedral and/or twist characteristics.
Another object of the present invention is to provide a free wing for rigid wing ultra-light aircraft having improved gust alleviation characteristics.
Still a further object is to provide an effective means for hinging a rigid wing to the hang cage so that the wing is free to rotate in pitch without effecting the dihedral and/or twist characteristics of the wing.
Yet another object is to provide a free rigid wing wherein bending or aerodynamically induced wing loads are converted into tension and compression loads distributed to other parts of the aircraft to minimize excessive wing loading.
A further object is to provide a free rigid wing in an ultra-light aircraft utilizing a simple, inexpensive yet reliable hinging mechanism for securing the wing to the aircraft.
Yet another object is to provide a simple, inexpensive yet reliable mechanism to assist in maintaining the dihedral and/or twist characteristics of the wing while simultaneously transferring excessive wing loading to the fuselage or hang cage as the wing rotates about the hinge to automatically vary its angle of pitch without pilot intervention in response to changes in flight conditions.